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<title>Using as: Xtensa Branch Relaxation</title>

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<a name="Xtensa-Branch-Relaxation"></a>
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<p>
Next: <a href="Xtensa-Call-Relaxation.html#Xtensa-Call-Relaxation" accesskey="n" rel="next">Xtensa Call Relaxation</a>, Up: <a href="Xtensa-Relaxation.html#Xtensa-Relaxation" accesskey="u" rel="up">Xtensa Relaxation</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Conditional-Branch-Relaxation"></a>
<h4 class="subsubsection">9.52.4.1 Conditional Branch Relaxation</h4>
<a name="index-relaxation-of-branch-instructions"></a>
<a name="index-branch-instructions_002c-relaxation"></a>

<p>When the target of a branch is too far away from the branch itself,
i.e., when the offset from the branch to the target is too large to fit
in the immediate field of the branch instruction, it may be necessary to
replace the branch with a branch around a jump.  For example,
</p>
<div class="smallexample">
<pre class="smallexample">    beqz    a2, L
</pre></div>

<p>may result in:
</p>
<div class="smallexample">
<pre class="smallexample">    bnez.n  a2, M
    j L
M:
</pre></div>

<p>(The <code>BNEZ.N</code> instruction would be used in this example only if the
density option is available.  Otherwise, <code>BNEZ</code> would be used.)
</p>
<p>This relaxation works well because the unconditional jump instruction
has a much larger offset range than the various conditional branches.
However, an error will occur if a branch target is beyond the range of a
jump instruction.  <code>as</code> cannot relax unconditional jumps.
Similarly, an error will occur if the original input contains an
unconditional jump to a target that is out of range.
</p>
<p>Branch relaxation is enabled by default.  It can be disabled by using
underscore prefixes (see <a href="Xtensa-Opcodes.html#Xtensa-Opcodes">Opcode Names</a>), the
&lsquo;<samp>--no-transform</samp>&rsquo; command-line option (see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>), or the <code>no-transform</code> directive
(see <a href="Transform-Directive.html#Transform-Directive">transform</a>).
</p>



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